While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 μm or less.
For resist materials for use with KrF excimer lasers, polyhydroxystyrene having a practical level of transparency and etching resistance is, in fact, a standard base resin. For resist materials for use with ArF excimer lasers, polyacrylic or polymethacrylic acid derivatives containing an adamantane structure in their side chain are often used as described in JP-A 9-73173 and JP-A 9-90637. Few of these polymers are regarded as exhibiting satisfactory performance.
More particularly, resist compositions using derivatives of polyacrylic or polymethacrylic acid as the base resin exhibit satisfactory sensitivity and resolution upon pattern formation by exposure and development, but have extremely low dry etching resistance. It is possible to improve the dry etching resistance to some extent by introducing many polycyclic structures as typified by adamantane structures to increase the carbon density. The resulting polymers, however, become highly hydrophobic as a whole, giving rise to undesired phenomena including pattern separation due to reduced substrate adhesion and development defects due to developer repellency. Still worse, the polymers substantially lose solubility in safe solvents such as propylene glycol monomethyl ether acetate. They are thus practically unacceptable. While a finer pattern rule is being demanded, there is a need to have a base resin for resist material which exerts satisfactory performance with respect to sensitivity and resolution, has practically acceptable etching resistance, and provides good adhesion to substrates, affinity to developers and solubility in solvents.